nuclear power plant

Nuclear power plant

Present India’s installed capacity of all sources power is 1,62,000 M.W. out of which 70 per cent power being produced through fossil energy sources and this energy sector getting saturated because of global attention towards cleaner energy sources . Alternative sources of energy will be renewable energy and nuclear energy. India significantly investing in wind power and solar energy while increasing generating capacity in hydel power.
Now nuclear power playing important role to reducing  global warming. In France Lithuania and china nuclear power is playing important role in their energy generation towards their countries development.

In France  nuclear  energy playing important role while France  generating 70 per cent of its power  through  nuclear energy. While U.S. 20 per cent power being generated through nuclear energy. Nuclear energy is clean source of energy without emitting any  carbon .

Nuclear power is an alternative method of generating in place where fossil fuel are  scarce or where hydroelectric sites unavailable nuclear power provides an alternative for generating large quantity.

Uranium is a strategic mineral  and western power have known for this start. Africa was most first important source of uranium even today.

From uranium mining and milling the uranium concentrate   is converted into uranium hexafluoride, as gas which is produced in order to enable uranium to be enriched.

Next step nuclear fuel chain, enrichment is also out hands of most developing countries. Strategic technology and only handful of countries have been able to get hold of technology. However enriched uranium needed for fueling the world’s most common nuclear reactors, the light modern the light water moderated plants.

Nuclear fission and Nuclear power plant

Every man from comic book writers  to theoretical physicists have characteristic the spitting atom as ultimate act of man playing god, so its easy to forget that nuclear fission happens naturally every day . Uranium for example constantly undergoes a spontaneous fission very slowly. This is a why element emits radiation and why its natural choice for induced fission that nuclear power plants requires.

Uranium is a common element on earth .It’s been around since planet formed uranium -238(U-238) has extremely long half-life (the time it takes for half its atoms decay ) 4-5 billion years. Therefore its still present in fairly large quantities U-238 make up 99 per cent uranium on the earth. While uranium-235 ( U- 235) make up about 0.7 per cent remaining  uranium found naturally . Uranium -234 is very rarer formed by decay of U-238 . U -238 goes through many stages of decay in its life span eventually forming a stable isotope  lead so U-234 is job one link in that chain.

Uranium U-235 has an interesting property that makes it handy for production both nuclear power plants and nuclear bombs. U-235 decays naturally, just as U-238 does by alpha radiation. It throws off an alpha particle or two neutrons and two protons  bound together . U-235 also under goes spontaneous fission a small percentage  of time. However U-235 is one of the few materials that can undergo induced fission. it’s a free neutrons runs into a U-235 nucleus the nucleus will absorb  the neutrons, becomes unstable and split immediately.

The animation of light shows a uranium -235 nucleus with neutron approaching  from top .The  probability of U-235 atom capturing a neutron as it passes by is high.Infact under reactor condition one neutron ejected from each fission causes another fission to occur.

As soon as nucleus captures the neutrons, it spits into two lighter atoms and throws off two or three new neutrons(the number of ejected neutrons depend  on how U-235 atom splits) .The process of capturing the neutrons and spitting happen very quickly on the order of picoseconds (1x10-12 second )

The decay of single U-235 atom releases approximately 200 MeV(million electron volts ) that may not seen like much but there are a lot of uranium atoms pound (0.45 kg) of uranium. So may,infact that pound of highly enriched uranium as used to power nuclear submarine is equal to about a million gallons of gasoline.

The spitting of atom releases an incredible amount of heat and gamma radiation or radiation made of high -energy photons . The two atoms that result from fission later release beta radiation (super fast electron ) and gamma radiation of their own as will. The energy released by single fission products and neutrons together ,weight less than original U-235 atom .The difference is weight converted directly to energy at a rate governed by equation E=  mc2

However  for all this work, a sample of uranium must be enriched so that it contains 2 to 3 per cent  U-235. Three per cent  enrichment is sufficient for nuclear power plants ,but weapons-grade uranium composed of at least 90 per cent of U-235.

Subcriticality,criticality and super criticality

When  a U-235 atom splits, two or three neutrons fly off. If there are no other  U-235 atoms around, then those free neutrons fly into space as neutrons rays. However if the U-235 atom is part of mass of uranium, then there are plenty of other U-235 atoms nearby for free wheeling neutrons to collide with. With one more of the free neutrons hit another U-235 atom ? The answer to that question determining a nuclear reactor status. 

Critical mass of average if on average exactly one of the neutrons  from each fission hits another U-235 nucleus and causes it to split then mass of uranium is said to be critical. The  mass will exist at a stable temperature.

Sub critical mass  : if on average ,less than one of the free neutrons hits other U-235 atom then the mass is sub critical. Eventually induced fission will end under these conditions and your source of power along with it.

Super critical mass  : if  on average more than one of the free neutrons hit another U-235 atom then the mass is super critical. This causes the reactor to heat up. 

In a nuclear reactor, however the last thing you (and rest of world) want is all your atoms spitting at once. But reactor core need to be slightly super critical so that plant operators can raise or lower the temperature of reactor. The control rods give operators a way to absorb free neutrons so operator  can maintain the reactor at a critical level.

The amount of U-235 in the mass( the level of enrichment ) plays a role ,as does the  shape of mass it self . If shape of mass is very thin sheet, most of free neutrons will fly off  into space rather the other U-235 atom. As such a sphere is optimal shape and you need 2 pounds (0.9 kg ) of  uranium U-235 atom in it to achieve a critical reaction. This amount therefore referred critical mass.

Inside nuclear power plant how works

To turn nuclear fission into electrical energy the first step for nuclear power plant operator is to be  able to control the energy given off by enriched uranium and allow it to heat water into steam.

Enriched uranium is typically formed in to inch long (2.5 cm long ) pellets each with approximately the same diameter as dim. Next pellets are arranged into long rods, and rods are collected together  into bundles. The bundles are submerged into water inside pressure vessels. The water acts as a coolant. For reactor  to work the submerged bundles must be slightly critical left to its own devices the uranium would eventually over heat and melt.
The problem overheating control rods made of material that absorb neutrons are inserted into uranium bundle using a mechanism that can raise or lower the control rods. Raising and lowering the control rods allow operators to control the rate of nuclear reaction. When operator wants the uranium core to produce more heat ,the control rods are raised out of uranium bundle this (absorbing fewer neutrons) .The rods can also be lowered completely into uranium bundle to shut the reactor down in the case of accident or to change the fuel.

The uranium bundle acts as an extremely high energy source of heat. It heats water and turn it into steam. The steam drive turbine which spurns a generator to produce power.

How steam technology works

In some nuclear power plants the steam from reactor goes through a secondary, intermediate heat exchanger to convert another loop of water to steam which drives the turbine. The advantage of this design is that the radio active water steam never contacts the turbine. Also in some reactors, the coolant fluid in contact with reactor core is gas (carbon dioxide) or liquid metal (sodium ,potassium ) these type reactors allow core to be operated at high temperatures.

By above information we understand how a nuclear reactor works.
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